1. Field
This disclosure relates generally to pressure transducers, and more specifically, to a pressure transducer having a structure for monitoring surface charge.
2. Related Art
Micro electro-mechanical systems (MEMS) components are used in a wide variety of applications. MEMS components are typically fabricated on semiconductor wafers using standard integrated circuit fabrication equipment. One type of MEMS component is a pressure transducer, or sensor. A MEMS pressure transducer is generally made by providing a substrate with a thin flexible diaphragm over a cavity. One or more piezoresistive elements are oriented on the diaphragm and electrically connected in, for example, a bridge configuration. The piezoresistive elements in the bridge change their resistance values in response to a bending of the diaphragm caused by pressure changes and thereby convert the sensed pressure to a corresponding electrical output signal such as a voltage or resistance. The surface of the diaphragm may be protected with a flexible material. However, during fabrication, packaging, handling, testing and field usage of the pressure transducer, a surface of the pressure transducer may become charged for various reasons before the flexible material is applied. Also, the sensor may be exposed to harsh environmental conditions that can apply a surface charge to the pressure sensor. The surface charge may form an inversion channel between conductive elements that contribute parasitic field effect transistor (FET) type leakage currents to the total current through the bridge. These parasitic FET contributions can induce changes in the operation of the piezoresistive elements, causing a shift of the output signal, and resulting in erroneous pressure readings without any indication to a user.
Therefore, what is needed is a pressure transducer that includes a structure for detecting accumulated surface charge.